1. Field of the Invention
The present invention relates to the field of materials processing, and more particularly, to the alignment of substrates such as semiconductor wafers on robot arms and in processing stations and, still more particularly, to the alignment of substrates, or wafers, of non-standard shape, for example, rectangular or, more broadly, right quadrilateral shaped wafers.
2. Description of the Prior Art
The production and quality control processes used by semiconductor device manufacturers and material producers often require a precise knowledge of such wafer characteristics, as wafer center and orientation, among others. Automated, high throughput assembly line like wafer checking systems are employed to obtain the desired information. The wafers must be aligned about their centers, and their flats selectively oriented in space, before being fed to the selected wafer characterization stations of a particular wafer checking system. In this regard, U.S. Pat. No. 4,457,664 to Judell et al. discloses a wafer alignment station that automatically aligns a wafer, having flats, about its centroid and orients the flats selectively in space which is suitable for use in automated production and quality control. The wafer alignment station suitably may be packaged in a module which is compatible for use with other wafer characterization stations in a high throughput material processing system.
For a number of years now, robot arms have been increasingly utilized for moving objects from one location to another. In the application of robotics to semiconductor wafer processing, a robot arm is useful for conveying a semiconductor wafer from one location to another through the use of independently controllable radial, circumferential and elevational motions. For many purposes, however, it is important that the wafer transported by the robot arm must be placed in a predetermined alignment with respect to its centroid and fiducial, if present.
According to the teaching of the inventions disclosed in U.S. Pat. Nos. 5,332,352 and 5,102,280 to Poduje et al., a robot arm is operative with an alignment station to adjust the orientation of a circular wafer or other element on the robot arm to a predetermined alignment for use by the robot arm in placing the wafer at a neighboring station in a desired orientation. According to the Poduje et al. disclosures, the robot arm includes a manipulator having independently controlled and isolated radial, circumferential and elevational motions, specifically, r, .THETA., z. A rotating support is provided within the range of placement for a semiconductor wafer carried by the robot arm and has associated with it an edge detector which determines the location of a wafer edge as it is rotated on the rotary support. The robot arm executes r, .THETA., z independent commands to cradle a wafer on its end effector or hand from a first location. The robot arm then places the wafer upon the rotary support where it is spun with the edge over the edge detector. The edge location is detected by electronics which determines the amount of motion of the centroid to produce alignment of the wafer on the rotary support and/or to locate the wafer fiducial in a predetermined location. The robot arm is then manipulated in a first case to move the wafer on the rotary support until alignment is secured with the fiducial relocated to a predetermined position. The wafer is again picked up by the robot arm for delivery to a further station in predetermined alignment. In a second case the robot arm is operative to pick up the wafer with the known misalignment and correct for such misalignment in delivering the wafer to a subsequent station.
It was with knowledge of the foregoing state of the technology that the present invention has been conceived and is now reduced to practice.